Power amplifiers for exciting plasma processes or laser discharge paths in a frequency range between 1 and 50 MHz, in particular at industrial frequencies of 13.56, 27.12, and 40.68 MHz are generally known. There are different power classes for power amplifiers of this type having output powers ranging from approximately 1 kW to several 100 kW. For a low power in the range between 1 and 20 kW, amplifiers on the basis of semiconductor modules (solid state amplifiers) are preferably used. Tube amplifiers are frequently used for a larger power. The tube amplifiers have an amplifier tube that is driven by a semiconductor power amplifier module, i.e., an amplifier that corresponds to amplifiers used for a smaller power. Since tubes require more space, it is desired to construct power amplifiers for larger output powers also of amplifiers based on semiconductor modules. Towards this end, solid state amplifiers of a smaller power are connected to suitable power couplers.
An important aspect of power amplifiers based on semiconductor modules is the minimization of the power loss, mainly in the semiconductor modules themselves. So-called amplifying circuits in resonance operation are advantageous, wherein the semiconductor modules are switched to have a particularly small loss.
Typical systems of switched amplifiers of classes D, E, and F are known, but a common problem of these switched amplifiers is the dynamically varying load. Such a load can develop in plasma processes and also in laser excitation or amplifier tubes, and the power supplied to the load can be reflected by the load. This reflected power is partially converted into heat by the amplifiers and is partly reflected back from the amplifier toward the load. Multiple reflections from load to amplifier and back produce instabilities in the amplifier and voltage and current increases, which can destroy the components in the amplifier and, in particular, also the semiconductor modules.
The output power of these amplifiers is usually controlled through control of the supplied direct voltage or direct current. If the power is to be rapidly controlled at the output, the supplied direct current must be rapidly controlled. This represents, however, also additional complexity for the direct voltage supply requiring expensive components and complex control.
Thus, a method and a control system for providing rapid and exact control with little power loss is desirable.